1. Field of the Invention
This invention relates to new aliphatic-cycloaliphatic diisocyanates containing a sterically hindered, cycloaliphatically bound isocyanate group in addition to a sterically unhindered, aliphatically bound isocyanate group, and to the use of the new diisocyanates as starting material for the preparation of polyurethanes.
2. Description of the Prior Art
The diisocyanates with aliphatically and/or cycloaliphatically bound isocyanate groups used in industrial polyurethane chemistry, e.g. 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane (isophorone diisocyanate), 4,4'-diisocyanato-dicyclohexylmethane or hexamethylene diisocyanate, are eminently suitable for the preparation of light-fast polyurethanes on account of their aliphatic character. These diisocyanates are therefore used in particular for the production of polyurethane lacquers or the production of lacquer polyisocyanates. One disadvantage of these important aliphatic and/or cycloaliphatic diisocyanates known in the art is to be seen in the fact that their isocyanate groups are identical or similar in their reactivity towards compounds containing isocyanate reactive groups. This gives rise to difficulties, for example, in reactions in which only one isocyanate group is intended to undergo reaction, e.g. in the preparation of isocyanate prepolymers by the reaction of one isocyanate group of the diisocyanate with hydroxyl groups of polyhydroxyl compounds of the type used in polyurethane chemistry.
It was therefore an object of the present invention to provide new aliphatic-cycloaliphatic diisocyanates in which the isocyanate groups should differ so distinctly in their reactivity as to enable isocyanate prepolymers having free isocyanate groups to be prepared without chain lengthening reactions occurring to any significant extent.
This problem was able to be solved by the preparation of the new diisocyanates according to this invention.